Torque Converter Question

[Rick B.]

A recent catastrophic rear thrust bearing failure on my meticulously rebuilt 454 has me researching possible causes.

As alignment and machining issues have been absolutely ruled out I am looking at the "original" torque converter as the possible culprit. Everything I have read suggests there has been alot of misunderstanding surrounding how excessive pressure can be created to push against the crankshaft and cause this wear on the bearing.

This leads me to ask the question "How do I identify whether my torque converter is original or even what it is exactly?" as there do not appear to be any discernible markings or part numbers upon it.

I have read all the threads on this site regarding this but while GM part numbers have been provided no one mentions if this number exists anywhere on the converter itself in order to identify what it is.

While I know more about the history of the car than most, there is a gap in this regard. The manner in which my car has always "loaded" the driveline harshly when placing it into "Drive" at idle suggests it may have a different stall speed characteristic than what the original one may have had. On the other hand I have nothing to compare it to and could be off base here.

Can anyone comment on any physical features/characteristics used to identify specific torque converters?


Thank you !

Rick

[Jim T.]

Re: Torque Converter Question

Rick I do not have a answer to your question concerning the torque converter and damage to your 454's thrust bearing. I do know that when installing a torque converter that it has to slip into the transmission and lock in. If this is not done, I don't know what the result would be.

[Joe L.]

Re: Torque Converter Question

A recent catastrophic rear thrust bearing failure on my meticulously rebuilt 454 has me researching possible causes.

As alignment and machining issues have been absolutely ruled out I am looking at the "original" torque converter as the possible culprit. Everything I have read suggests there has been alot of misunderstanding surrounding how excessive pressure can be created to push against the crankshaft and cause this wear on the bearing.

This leads me to ask the question "How do I identify whether my torque converter is original or even what it is exactly?" as there do not appear to be any discernible markings or part numbers upon it.

I have read all the threads on this site regarding this but while GM part numbers have been provided no one mentions if this number exists anywhere on the converter itself in order to identify what it is.

While I know more about the history of the car than most, there is a gap in this regard. The manner in which my car has always "loaded" the driveline harshly when placing it into "Drive" at idle suggests it may have a different stall speed characteristic than what the original one may have had. On the other hand I have nothing to compare it to and could be off base here.

Can anyone comment on any physical features/characteristics used to identify specific torque converters?


Thank you !

Rick

Rick-----


As with most parts in the GM of the "old days" torque converters were almost never stamped with any identifying numbers. This was "absurd" but that's how it was. The only way to identify a torque converter is to remove it from a KNOWN original application of a KNOWN part number OR buy a GM SERVICE converter in a box with a part number on it. One "clue", though, is this: GM torque converters are rarely, if ever, painted. If yours is painted, then you know it's either not a GM torque converter or it's a GM piece that's been "rebuilt" or "re-worked" by a non-GM entity.

The last available GM SERVICE torque converter for your application, GM #8656943, is long-since discontinued.

Even if you knew the part number of your torque converter, you still would not know it's internal condition. If I were you and I had any question regarding a torque converter, I'd do my best to find a NEW or quality reconditioned unit which was equivalent to the original converter in ALL functional respects. I would not want any kind of a "hot rod" or "modified" torque converter.

There were several supercessive part numbers for the GM torque converter for your application over the years. You want one exactly equivalent to any of the following:

GM #8623990 (the original part number)

GM #8627946

GM #8627945

GM #8656943

[Rick B.]

Re: Torque Converter Question

Jim, yes I had been forewarned about the incorrect positioning of the converter when doing the install - it can ruin the transmission drive pump and contribute to this condition however I made sure the appropriate amount of clearance existed between the plate and the converter to say with certainty this was not the case.

Joe, thankyou for your comments.
As my converter has been painted black ( albeit very poorly) I therefore suspect it is not the original one. I have an appointment this morning to have its' case cut open ( a converter autopsy ) to ascertain what may have been wrong with it and also to try and figure out approx. what stall speed it was providing so as to better modify the replacement. As my compression had been moderately increased and improvements made internally to provide at least an extra 85 true honest-to-gosh H.P. over the original specs of that engine, may I ask why you would not recommend changing out from any of the original converter specs? I was not entirely happy with the performance of my car "off-the-line" and felt it could be improved by a slightly increased stall speed ( nothing dramatic ) such as 2200. For the sake of driveability and economy I was not going to entertain anything more radical than that. What are your thoughts?

Thanks, Rick

[Joe L.]

Re: Torque Converter Question

Jim, yes I had been forewarned about the incorrect positioning of the converter when doing the install - it can ruin the transmission drive pump and contribute to this condition however I made sure the appropriate amount of clearance existed between the plate and the converter to say with certainty this was not the case.

Joe, thankyou for your comments.
As my converter has been painted black ( albeit very poorly) I therefore suspect it is not the original one. I have an appointment this morning to have its' case cut open ( a converter autopsy ) to ascertain what may have been wrong with it and also to try and figure out approx. what stall speed it was providing so as to better modify the replacement. As my compression had been moderately increased and improvements made internally to provide at least an extra 85 true honest-to-gosh H.P. over the original specs of that engine, may I ask why you would not recommend changing out from any of the original converter specs? I was not entirely happy with the performance of my car "off-the-line" and felt it could be improved by a slightly increased stall speed ( nothing dramatic ) such as 2200. For the sake of driveability and economy I was not going to entertain anything more radical than that. What are your thoughts?

Thanks, Rick

Rick------


Well, first of all, I thought that the engine was more-or-less completely stock. A tremendous amount of engineering goes into matching the stock converter with the stock engine. Trying to "second-guess" that is an exercise in complete, "unaldulterated" futility.

Even with an engine modified to the degree you've described, if it were me I'd still go with a stock converter. With a "modified" or "high perf" converter, you may gain in some areas of performance but you'll lose in other areas. The factory devotes a lot of very expensive engineering effort to obtain the best BALANCE of performance, driveability, DURABILITY, etc. Why "toss that all out" in favor of engineering done by an aftermarket outfit on a "shoestring" budget?

Don't misunderstand, though. There are times when factory engineering can be improved upon. However, one has to be very selective and judicious in judging just when such opportunities exist.

[Edward J.]

Re: Torque Converter Question

Rick, there are only a few things that can cause a thrust bearing to fail, one is the improper install of the torque convertor (not fully engaged)

And the other is if the crankshaft was machined poorly excessive clearance on the thrust sides, when the bearing fails, it generally both side of the bearing that have failed, when its a improperly installed torque convertor, it generally the one side of the bearing that has failed due to constant pressure on one side of the brg.

As far as the torque convertor stall speed you want to install, I would let a qualified trans expert rebuild the assy. and install what mods would be required along with the performance convertor. The THM400 does have the greatest power loss of the 3 speed trans. and there are many improvements that can be made to get you the performance along with the durabilty you want, and they are generally not as costly as the tansmissons of today. or just leave it stock and receive great durabilty from the 400THM.

[Rick B.]

Re: Torque Converter Question

Thank you.
I agree with all of your comments.
Crank tolerances were checked before and after and were fine, only one side of the bearing failed and the torque converter was installed properly (verified independently as I was forewarned about the consequences of not properly seating the converter upon install. )
I have to laugh though, the experiences I have had with "qualified transmission experts" has been non-existent. Unfortunately there seems to be very few of those people around and even fewer that you can identify by talking to them.
For the record the examination of the inside of my converter showed nothing abnormal. It was in fact a rebuilt model which suggests that it was replaced when the tranny was rebuilt by the previous owner.
When asked if they could ascertain the approx. stall speed of this particular converter they said it was probably around 1800. There most certainly appears to be no definitive way to quantify this elusive term other than by using general numbers as they admit to significant variances.
I will continue to sleuth and won't give up on examining the engine until I find the culprit as I don't want to repeat this adventure again. I may even pull the tranny now and have someone examine it just to be safe.
Thanks again for your input.
Rick

[Terry M.]

Re: Torque Converter Question

Rick,

I'm not making excuses for the trans shop, but a TH400 is an antique by today's trans shop standards. That is not to say they shouldn't be able to do a good job, although some may take on work they are not qualified to do. You will be better off trying to find a place that has been in business for a long time, and ask if they have anyone "up in years."

Back in the day there was a measurement for the overall length of a torque convertor, but it was not to my knowledge in any of the factory TH literature. If one boosts the line pressure, and has a TC with higher stall speed; the chances of ballooning the TC are greater than with stock settings and equipment. That is just one of the reasons Joe, and I, favor stock rebuilds. The number of clutches and friction plates should be maximized to duplicate the "CY" configuration. Now finding someone who knows about that is another matter. Good luck.

[Edward J.]

Re: Torque Converter Question

Rick, which end of the thrust brg. failed? Closest to the flywheel or harmonic balancer side.

[Rick B.]

Re: Torque Converter Question

Wear can be seen on both sides of the bearing. Adequate clearance was checked when buttoning the engine up - the slop developed in the first 100 miles and was picked up when I saw the mass of gold (bright brass) colored filings in the oil. The oil was significantly darkened indicating excessive heat caused by the friction of that failed bearing. All other surfaces perfect.

Rick

[Terry M.]

Re: Torque Converter Question

Dumb question here, so I apologize in advance.
I remember something about lightly tightening the main cap with the thrust bearing and the whacking the crank once to the front, and once to the rear -- then torquing the main bolts for the cap with the thrust bearing. That is to align both halves of the bearing. Was the wear equal on both halves of the bearing?

[Edward J.]

Re: Torque Converter Question

Rick,, the reason I asked was while installing the harmonic balancer I was wondering if if was started with a hammer, as I know I have seen it done, which can result in the rear half of the bearing to be damaged and this is the start of a thrust brg. problem.